Currently, time consuming, labor intensive procedures are used to detect, faulty fuel systems of internal combustion engines. These procedures require external testing equipment to be attached to the engine. Although U.S. Pat. No. 5,455,019 discloses an on-board diagnostic system for detecting impaired fuel injectors of a fuel delivery system thereby obviating the need for external testing equipment, problems exist with the system disclosed in the '019 patent. As used herein, "on-board" means that the instructions or program necessary to perform the test is encoded within a computer that controls the engine, typically referred to as a powertrain control module (PCM) or an electronic engine controller (EEC). Generally, the system disclosed in U.S. Pat. No. 5,455,019 initiates a test whereby each fuel injector is actuated and the pressure in the fuel rail near the fuel injector is monitored. This pressure is then compared to a pressure range stored within the memory of the PCM. If the monitored pressure is within the specified range, then the injector is functioning properly. If not, the faulty injector is repaired or replaced accordingly.
In U.S. Pat. No. 5,455,019, the system performs the diagnostic test while the engine is running and uses a high cost pressure transducer. This results in undesirable pressure pulses because of the overlap of the pressure waves from one injection event to the next while the engine is running. A software algorithm is used to separate the pulses by intruding on normal engine running strategy and momentarily shutting off the fuel to the injectors.